Segmented ring-type refractory metal liners for guns



R. F. BAKER March 20, 1962 SEGMENTED RING-TYPE REFRACTORY METAL LINERS FOR GUNS Filed Jan. 50, 1952 It r1 wi h IIIHI.

Viva/ W INVENTOR F. F 3fl/ B 3,625,765 Patented Mar. 28, 1962 lice 3,025,765 SEGMENTED RING-TYPE REFRACTQRY METAL LHNERS FUR GUNS Robert F. Baker, Butler, Ni, assignor to Westinghouse Electric (Iorporation, East Pittsburgh, Pin, a corporation of Pennsylvania Filed Jan. 30, 1952, Ser. No. 268,974 2 Claims. (Cl. 89]l6) This invention relates to precision forging of tubular and other bodies, such as guns and exhaust tubes for jet engines and, more particularly, to liners for such tubular bodies and methods of forging, but may be adapted to many other applications requiring refractory metal of special shapes and precise dimensions.

The principal object of my invention, generally considered, is to provide segmented ring-type refractory metal liners for guns and other tubular bodies, with the refractory metal parts connected to one another by circumscribed metal of a different character and/or to the carrier forming the gun barrel by welding and/ or shrinking the latter over the assembled parts.

Another object of my invention is to forge a button of molybdenum or the like inside a ring of steel or similar material, whereby the dimensions thereof may be reproduced repeatedly within very close tolerances.

A further object of my invention is to Overcome weaknesses in assemblies of molybdenum liners with steel gun barrels by avoiding connecting pins, grooves or sharp notches.

A still further object of my invention is to reduce the wastage of molybdenum and similar materials, as well as time-consuming machining to produce the required tolerances in the making of parts.

An additional object of my invention is to manufacture parts consisting of worked molybdenum and alloys thereof, as subsequently defined, and corresponding or similar refractory metal, by distorting a merely pressed and sintered ingot, made from such material in powdered form, at an elevated temperature, to reduce its axial length and cause it to expand outwardly into engagement with a circumscribing ring of steel or the like, whereby a part of molybdenum of exact dimensions may be conveniently produced simultaneously with effective working thereof, and the circumscribing steel portion may serve for connecting it to a carrier or associated part, such as the barrel of a gun if used as a gun liner.

Another object of my invention is the manufacture of gun liners of molybdenum and alloys thereof by pressing the metal as powder into cylindrical form, sintering, heating to about 1200" C., and pressing down axially thereon to expand it inside of a steel ring desirably having longitudinal and circumferential grooves which lock it in place therein, turning the ends of the part so formed to the ength of the ring, or the diameter of the ring to match the molybdenum portions extending therebeyond, drilling to produce the desired axial aperture of the proper caliber, threading on a mandrel, tightly holding the parts together by a nut or nuts, turning to finished dimension, cooling, inserting in a carrier or gun barrel, and effecting a shrink fit therebetween.

Other objects and advantages of this invention will become apparent as the description proceeds.

Referring to the scale drawing:

FIGURE 1 is a vertical axial sectional view of one embodiment of apparatus for practicing my invention, including a pressed and sintered ingot of molybdenum in place ready to be worked and expanded to desired assembly with a steel ring.

FIGURE 2 is a view corresponding to portions of FIGURE 1 but showing the ingot after having been axially deformed to cause it to expand, fill, and consolidate itself with, the surrounding steel ring.

FIGURE 3 is a perspective view of the steel ring before assembly with the ingot, in order to show the inside grooves to effect locking with said ingot.

FIGURE 4 is a view corresponding with FIG. 2, but showing the ring and ingot assembly after trimming the excess of the ingot which protrudes beyond the ends of the ring.

FIGURE 5 is a view corresponding with FIG. 4 but showing the ring and ingot assembly after trimming the ring to correspond with the diameter of the ingot ends.

FIGURE 6 is an axial sectional view of a gun barrel or carrier enclosing a series of rings forming a gun liner embodying my invention.

FIGURE 7 is view corresponding to a part of FIGURE 1, but showing the employment of a hollow ingot of molybdenum or the like filled with a cylinder of steel or similar material, in order to conserve refractory metal, the parts being shown in a position of partial forging.

Molybdenum has a lower coefiicient of expansion than steel. For this reason when a tube of molybdenum is fastened in a steel gun barrel, or as a gun liner, and the barrel or carrier becomes very hot as during firing, the steel expands away from the molybdenum liner and there is a gap left therebetween. In order to make the liner expand as much along the length of the gun or carrier as its steel carrier during firing, such have been made of rings individually fastened to the steel, so that large gaps do not form, and so that other undesirable effects, due to differences in thermal expansion, may not take place.

Ring-type liners have been experimentally tested and it has been found that longitudinal cracking takes place, where such liners are made composite with steel portions and connected thereto by steel pins, where the molybdenum is thin over the pins. In accordance with my invention, however, I avoid the use of any separate connecting means, such as pins, between the molybdenum and the steel by other portions secured thereto to allow for the difference in expansion between the molybdenum and the steel, and to serve as connecting means between the liner rings, and between said rings and their carrier.

Each liner ring, according to my invention includes, with specific reference to the drawing, a hollow relativelyshort, in this embodiment about in axial dimension, generally cylindrical portion formed of molybdenum or alloy thereof with small proportions of metal selected from the group consisting of cobalt, nickel, iron and tungsten that is, in which the proportion of any of the first three alloying metals is not greater than and in which the proportion of the alloying tungsten is not greater than 15%. Using higher temperatures, it may alternatively be formed of tungsten or a corresponding alloy thereof. The inner cylindrical surface is of diameter corresponding with the bore desired. The outer cylindrical surface of each ring is formed to interlock with a carrier ring portion of steel or the like.

Referring now to FIGURE 1, there are shown parts of a hammer or press comprising a lower die block 11 and an upper die block 12. Resting on the lower die block is an assembly of steel annular members or rings supported on said block 11 by an annular soft rubber cushion 14, in the present embodiment desirably A" x in section, set in the lower face thereof, and of such a size as to hold the assembly a slight distance, say about /8" above the block. The annular pocket which receives said cushion is countersunk, as indicated at 15, to allow for reception of the rubber as it expands upon further compression.

In the present embodiment, to scale for making a 50 caliber gun, the assembly consists of an inner ring 16, desirably formed of S.A.E. #4140 gun steel. A preferred embodiment is one with about Ms" inside diameter by 1%" outside diameter, by .525" long. This ring directly encircles an ingot or button 17 of molybdenum or other alternative aforementioned. This ingot is formed by pressing and then sintering the powdered metal, in accordance with conventional practice, no previous working being necessary. This ingot, for a .50 caliber gun, is about .625" in diameter by about 1.25 long or high. The dimensions are determined by calculation as well as by trial. A slight variation in either dimension may be tolerated.

In order to prevent undesired expansive deformation of the ring 16 when the ingot or button 17 is pressed down by the die block 12, said ring is fitted inside a ring 18, the fit being just tight enough to prevent it dropping out when both parts are at the same temperature. The ring 18 is about 2%" in outside diameter, about .55 long, and desirably formed of No. 21 tool steel, Westinghouse Purchasing Dept. Spec. 7900, Rockwell hardness, C-40 to 45.

The ring 18 is, in turn, backed by a ring 19 of similar material about 4" in external diameter and shrunk thereover after forming said rings with .006 interference when at the same temperature. That is, there is that much difference between the external diameter of the ring 18 and the internal diameter of the ring 15*. Backing the ring 19 is an outer ring 21, desirably formed of S.A.E. #4140 gun steel, Westinghouse Purchasing Dept. Spec. 7940, Rockwell hardness, (2-30 to 35. This ring has an external diameter of 6", a length also of .55 and the interference between it and ring numbered 19 when at the same temperature is .008". That is, there is that much difference between the outer diameter of ring 19 and the inner diameter of ring 21, so that an appropriate shrink fit therebetween may be effected.

The size of the ingot 17 may be varied slightly, thereby giving more or less overflow 22 when it is squeezed in position in the ring 16, as viewed in FIGURE 2. In the same Way, the size of the ingot and the lengths and/ or diameters of the rings 16, 18, 19 and 21 are correspondingly varied with variation in gun caliber. For example, if the caliber of the gun being made is .60 rather than .50, the size of the ingot 17 is increased to .7" diameter by 1.4" long or high, the inner and outer diameters of the ring 16 are respectively increased to 1" and 1%", while the length and outer diameters of rings 18, 19 and 21 remain unchanged.

If the caliber of the gun being manufactured is 20 mm., while the outer diameters of the rings 19 and 21 are unchanged, the outer diameter of the ring 18 is increased to 3", and that of the ring 16 to 1.312" while its inner diameter is increased to 1.156". If the gun being manufactured is 40 mm., the outer diameter of the ring 21 is desirably 7%"; that of the ring 19, that of the ring 18, 4%"; that of the ring 16, 2%", its inner diameter being 2.15"; with the thickness of all rings increased to and the mean diameter of the rubber supporting member 14 increased from 5" to 6 /4".

In order to insure that the molybdenum ingot 17, when squeezed into ring 16, is locked in place therein against relative axial and turning movement, there are desirably formed a circumferential groove 23 and four equally spaced longitudinal grooves 24 on the inner surface of the ring 16, so that as the ingot is squeezed in place portions thereof fill said grooves and provide secure locking therebetween.

Although I have shown grooves to effect such interlocking, such grooves being shown intersecting and forming indentations connected around the periphery, it will be understood that I do not wish to be limited to this construction, as the indentations or grooves may be T or inverted T-shape in appearance, or may involve segmented or separated circumferential indentations, that is, alternately longitudinal and circumferential around the periphery.

Alternatively, the configuration may be reversed, that is, ridges positioned like the grooves 23 and 24, providing in any event areas lying on different cylindrical surfaces. Sharp corners are avoided in the grooves or at the ridges, which are desirably .015" deep and about A" wide. The surfaces defining said grooves or ridges are desirably formed about an approximately A radius.

The operation of forming the assembly illustrated in FIG. 2 is as follows. The parts are assembled as illustrated in FIG. 1, with the button 17 heated to an appropriate forging temperature, which for molybdenum is about 1200 C. When the .upper forging die hits the button it is reduced in height and immediately assumes a barrel shaped appearance. This continues until the molybdenum contacts the steel ring 16. The ideal condition at this point is to have the medial periphery of the button contact the inner surface of the steel ring midway between its top and bottom. The strength of the steel ring supported by the very strong assembly will not permit any further diametrical expansion. The molybdenum must flow in some direction under the impact of the hammer. Therefore, the top and bottom of the button begin to bulge. This bulging continues until the entire length of the steel ring has been filled and the molybdenum over-' fills on top and bottom. Since the height reduction of the molybdenum is very rapid it is necessary to support the assembly above the bottom die to insure complete fill at the bottom. The rubber ring 14 readily flattens out permitting the excess molybdenum on the bottom to flow against and over the steel ring.

The molybdenum button loses its heat immediately on contact with the steel ring. The heat absorbed by the steel ring causes it to expand. Since it cannot expand outwards until the assembly heats, it must increase slightly in length. By quenching the entire assembly with water after forging, the steel ring will contract sufficiently to permit the molybdenum button and the steel ring to be easily pressed out of the assembly. The heating and cooling of the steel ring produces an even tighter fit between the molybdenum and the steel. Other than boring a hole in the molybdenum-steel segment and facing off the ends to the desired length, there is no further machining required on the molybdenum.

The pressing of the ingot 17, from the shape illustrated in FIGURE 1 to that of FIGURE 2, effects the necessary working of the metal, whereby it is permissible to use an ingot of a merely pressed and sintered metal powder. Although molybdenum has been specifically discussed, the ingot may be formed of an alloy or of tungsten, as previously suggested. Also, other steels than #4140, such as #4130 or #4150, and other metals than iron or steel, including nickel-plated steel, may be employed. Such plating, if employed, improves the bond between the ingot to the ring.

In order to prepare the assembly of FIGURE 2 for insertion in a gun barrel or other carrier 25, as illustrated in FIGURE 6, the bulging portions 22 are trimmed off so that the axial dimension of the molybdenum or the like corresponds with that of the ring 16 to form a structure illustrated in FIGURE 4. This structure is then drilled to produce the desired axial aperture 26, corresponding with the caliber of the gun being manufactured.

A series of such assemblies are then threaded on a mandrel 27, where they are tightly held together as by a nut or nuts 28. After welding said assemblies together, if desired, they are placed in a lathe and turned and ground to finished dimension and taper (if employed). They are secured in the carrier in any desired manner including shrink fitting. This may be accomplished by cooling the assemblies, as by liquid air, heating the gun barrel or carrier 25, or both, prior to insertion therein, where they are allowed to regain the same temperature to effect a shrink fit with said barrel.

As an alternative, the assembly as illustrated in FIG- URE 2, may be turned to trim the ring 16 to a diameter corresponding with that of the overfiow 22 of the molybdenum beyond the ends thereof, and as viewed in FIG- URE 5. The succeeding operations are otherwise identical except, of some," that in this case the diameter or the ring 16 is initially correspondingly larger for a given caliber of gun than is necessary when the trimming is at the ends rather than around the circumference.

Referring now to the embodiment of my invention illustrated in FIGURE 7, there are shown parts of a hammer or press, similar to that of FIGURE 1, comprising a lower die block 11 and upper die block 12 Resting on the lower die block is an assembly of steel annular members or rings supported on said block 11 by an annular soft rubber cushion, not shown but similar to that designated 14 in FIGURE 1. This assembly may be identical or equivalent in strength to that shown in FIGURE 1 and include an inner ring 16 desirably formed of the same kind of material as that of the ring 16. This ring, as in the preceding embodiment, directly encircles an ingot or button 17 of molybdenum and other alternative aforementioned.

In this case, however, the ingot instead of being formed solid cylindrical, is formed hollow cylindrical and the interior initially plugged by a cylinder 23 of steel, brass, or other such material, suitable because it is cheap and of not too low melting point, so that it is solid at a forging temperature of about 1200" C., for example, if used with a molybdenum ingot. The use of a filling or plug of relatively cheap metal in a hollow molybdenum or tungsten ingot to prevent collapse during forging is particularly advantageous when ingots of relatively large size are being forged, to save a relatively-large quantity of the more expensive refractory metal.

FIGURE 7 shows the ingot ll7 only partially forged. The initial construction compares closely with that of the ingot 17 in FIGURE 1, except that it is hollow and plugged, rather than solid as there shown. The final form of the ingot after complete forging agrees generally with that of FIGURE 2, except that the inside, instead of being molybdenum, is a rounded mass of steel or other filling material, generally like that designated 23' in FIGURE 7. Another advantage of this use of a hollow, rather than a solid, ingot is also a greater working of the refractory material, and particularly a working on the inner surface. After complete forging, the steel or other relatively cheap metal may be removed by drilling or dissolving it therefrom, and finishing the interior of the ingot to the desired diameter or caliber.

In designing ingots, such as those designated 17 and 17*, it is important that the height or length thereof be not more than about twice the diameter, so that they will stay vertical during pressing, avoiding undesired distortion due to column effect. In other Words, a preferred ratio between height and diameter is 2 to 1.

Although I have described a built-up or three-piece backing for the ring 16, yet I do not wish to be limited to this construction, as the only essential requirement is that the backing be suficiently strong to avoid expansion during the forging operation. In other words, if a strong er steel is employed, the size of the backing may be smaller, or of a number of pieces different from three.

However, one of the major problems has been in preventing the retained ring 18 from expanding internally with successive forging. This has, however, been solved by developing a strong structure and by controlling the volume of the molybdenum or other refractory metal forged into the steel rings. There must not be any increase in the inside diameter of the retaining die or ring 18 as it would then not be possible to forge continuously, that is, a number of steel rings 16 could not be prepared having the same outside diameter to fit the inside diameter of the retaining die 18 if this dimension were to change.

Although I have disclosed a method and apparatus for producing hollow cylindrical liner rings, yet I do not wish to be limited to this, as my invention may be employed for making other shapes, such as solid or hollow tapered members of molybdenum or other refractory material, by making the ring 16 with a corresponding internal taper rather than hollow cylindrical. I may also forge refractory metal in ring 16 of the desired internal size and shape, while in engagement with the lower die block 11, rather than positioned thereabove. If this is done, however, there is no overflow beneath the ring but only above, thus developing hat-shaped forgings or those with flanges at the top only. In other words, my method of forging is suitable for making practically any shape by just forging a suitably heated ingot of merely pressed and sintered refractory metal powder of suitable volume into a suitably-backed ring or die of the desired shape.

From the foregoing, it will be seen that I have devised an improved liner segment and gun liner, avoiding the use of pins or other auxiliary or separate connecting elements and, instead, using shallow grooves or ridges in the interior surface of a ring in which an ingot of the refractory metal is upset. The elements of the gun liner may not only be connected to the gun barrel by a shrink fit but also connected to one another as by welding between the carrying rings, which welding may be effected while on a mandrel and prior to turning and/or grinding to finished dimension. The finished dimension is of course slightly larger than the inside diameter of the gun barrel or carrier, providing the necessary interference in effecting the desired shrink fit.

By die pressing, molybdenum buttons can be fabricated within close tolerance of the desired starting size. Approximately four times as many buttons can be made as are now obtainable from rolled flats using the same amount of powder. The time and cost of fabrication of gun liner segments is greatly diminished in almost every step of their fabrication. It is possible to adapt these procedures to a production basis whereby automatic equipment could be utilized. A forging press may be substituted for the forging hammer.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications are contemplated. The terms molybdenum and tungsten as used in the claims include alloys thereof as herein defined, and by the term forging I include quickpressing to the desired extent in one stroke between the dies of a hammer or press, and by the term pressing," as applied to the ingot, I include forging.

I claim:

1. In a gun, a hollow steel carrier, a liner therein consisting of a series of hollow cylindrical portions formed as steel rings and having circumferential and longitudinal grooves on their respective inner peripheral surface with portions of refractory metal selected from the group consisting of molybdenum and tungsten pressure-fitted into the surrounding steel ring and interlocking in said grooves, with the inside diameter of said hollow portions corresponding with the caliber of the gun, the outside diameter of the steel rings corresponding with the inside of said carrier, and said steel rings serving to connect said refractory metal portions together and to said carrier.

2. In a gun, a hollow steel carrier, a liner therein comprising a series of hollow cylindrical ring portions motion therebetween, s'aid steel ring serving to connect 5 said liner portions together and to said carrier.

References Cited in the file of this patent UNITED STATES PATENTS 47,177 Ames Apr. 11, 1865 4% Emery Apr. 28, Morgan et a1 Nov. 4, Malaval et a1. June 30, Lemming Apr. 13, Traversi et a1. A151". 15, Lowit Apr. 10, Taylor Aug. 14, Brace et a1. Mar. 7,

FOREIGN PATENTS Sweden 1 June 22, 

2. IN A GUN, A HOLLOW STEEL CARRIER, A KINER THEREIN COMPRISING OF STEEL, THE INNER SURFACES OF WHICH ARE GROOVED FORMED OF STEEL, THE INNER SURFACES OF WHICH ARE GROOVED CIRCUMFERENTIALLY AND LONGITUDINALLY, EACH RING BEING LINED WITH MOLYBDENUM PRESSURE-FITTED IN PLACE SO THAT PORTIONS THEREOF INTERLOCK IN SAID GROOVES TO PREVENT RELATIVE MOTION THEREBETWEEN, SAID STEEL RING SERVING TO CONNECT SAID LINER PORTIONS TOGETHER AND TO SAID CARRIER. 